Re: emergency or init=/bin/sh mode and terminal signals

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

David Luyer, le Tue 20 Jun 2006 10:02:23 +1000, a écrit :
> On 20/6/06 8:09 AM, "Samuel Thibault" <samuel.thibault@ens-lyon.org> wrote:
> > linux-os (Dick Johnson), le Mon 19 Jun 2006 07:37:02 -0400, a écrit :
> >> You can't allow some terminal input to affect init. It has been the
> >> de facto standard in Unix, that the only time one should have a
> >> controlling terminal is after somebody logs in and owns something to
> >> control.
> > 
> > Ok. The following still makes sense, doesn't it? (i.e. set a session for
> > the emergency shell)
> > 
> > --- linux-2.6.17-orig/init/main.c 2006-06-18 19:22:40.000000000 +0200
> > +++ linux-2.6.17-perso/init/main.c 2006-06-20 00:07:07.000000000 +0200
> > @@ -729,6 +729,11 @@
> > run_init_process("/sbin/init");
> > run_init_process("/etc/init");
> > run_init_process("/bin/init");
> > +
> > + /* Set a session for the shell.  */
> > + sys_setsid();
> > + sys_ioctl(0, TIOCSCTTY, 1);
> > +
> > run_init_process("/bin/sh");
> >  
> > panic("No init found.  Try passing init= option to kernel.");
> 
> What if people are booting via /bin/sh and then setting up
> their custom chroot's and init(s), and don't want these init(s) to
> be part of a session?

The problem is that you can't distinguish that from usual init booting:

	if (execute_command) {
		run_init_process(execute_command);
		printk(KERN_WARNING "Failed to execute %s.  Attempting "
					"defaults...\n", execute_command);
	}
	run_init_process("/sbin/init");

If you setsid() in the if(execute_command) statement, and the
execute_command fails, you get to run init in a session.

> It is also particularly possible for an embedded system to start
> up via /bin/sh running /etc/profile rather than using an init type
> program.

Then people writing that embedded system should use /bin/login instead.

> Also, the above doesn't help people specifying "init=/bin/sh" on the
> command line (as per the original post subject).  The real solution
> is for them to specify a different init= or run/exec something to set
> up their tty and session once logged in.

Yes. And the problem is that people usually don't know about sessions
etc, and will just grumble "linux can't work".

Samuel